1. Field of the Invention
The present invention relates to an ink-jet printhead. More particularly, the present invention relates to a bubble-jet type ink-jet printhead having a hemispherical ink chamber and a manufacturing method thereof.
2. Description of the Related Art
Ink-jet printing heads are devices for printing a predetermined color image by ejecting small droplets of printing ink at desired positions on a recording sheet. Ink ejection mechanisms of an ink-jet printer are generally categorized into two types: an electro-thermal transducer type (bubble-jet type), in which a heat source is employed to form a bubble in ink causing an ink droplet to be ejected, and an electromechanical transducer type, in which a piezoelectric crystal bends to change the volume of ink causing an ink droplet to be expelled.
FIG. 1A is a cross-sectional, perspective view showing an example of the structure of a conventional bubble-jet type ink-jet printhead as disclosed in U.S. Pat. No. 4,882,595. FIG. 1B is a cross-sectional view illustrating a process of ejecting an ink droplet from the printhead of FIG. 1A. The conventional bubblejet type ink-jet printhead shown in FIGS. 1A and 1B includes a substrate 10, a barrier wall 12 disposed on the substrate 10 for forming an ink chamber 13 filled with ink 19, a heater 14 disposed in the ink chamber 13, and a nozzle plate 11 having a nozzle 16 for ejecting an ink droplet 19xe2x80x2. The ink 19 is introduced into the ink chamber 13 through an ink feed channel 15, and the ink 19 fills the nozzle 16 connected to the ink chamber 13 by capillary action. In a printhead of the current configuration, if current is supplied to the heater 14, the heater 14 generates heat to form a bubble 18 in the ink 19 within the ink chamber 13. The bubble 18 expands to exert pressure on the ink 19 present in the ink chamber 13, which causes an ink droplet 19xe2x80x2 to be expelled through the nozzle 16. Then, ink 19 is introduced through the ink feed channel 15 to refill the ink chamber 13.
There are multiple factors and parameters to consider in making an ink-jet printhead having a bubble-jet type ink ejector. First, it should be simple to manufacture, have a low manufacturing cost, and be capable of being mass-produced. Second, in order to produce high quality color images, the formation of minute, undesirable satellite ink droplets that usually trail an ejected main ink droplet must be avoided. Third, when ink is ejected from one nozzle or when ink refills an ink chamber after ink ejection, cross-talk with adjacent nozzles, from which no ink is ejected, must also be avoided. To this end, a backflow of ink in a direction opposite to the direction ink is ejected from a nozzle must be prevented during ink ejection. Fourth, for high speed printing, a cycle beginning with ink ejection and ending with ink refill in the ink channel must be carried out in as short a period of time as possible. That is, an operating frequency must be high. Fifth, the printhead needs to have a small thermal load imposed due to heat generated by a heater and the printhead should operate stably for long periods of time at high operating frequencies.
The above requirements, however, tend to conflict with one another. Furthermore, the performance of an ink-jet printhead is closely associated with and affected by the structure and design of an ink chamber, an ink channel, and a heater, as well as by the type of formation and expansion of bubbles, and the relative size of each component.
In an effort to overcome problems related to the above requirements, ink-jet printheads having a variety of structures have been proposed in U.S. Pat. Nos. 4,339,762; 5,760,804; 4,847,630; and 5,850,241 in addition to the above-referenced U.S. Pat. No. 4,882,595; European Patent No. 317,171; and Fan-Gang Tseng, Chang-Jin Kim, and Chih-Ming Ho, xe2x80x9cA Novel Microinjector with Virtual Chamber Neck,xe2x80x9d IEEE MEMS ""98, pp. 57-62. However, ink-jet printheads proposed in the above-mentioned patents and publication may satisfy some of the aforementioned requirements but do not completely provide an improved ink-jet printing approach.
FIG. 2 illustrates a back-shooting type ink ejector of another example of a conventional bubble-jet type ink-jet printhead, as disclosed in IEEE MEMS ""98, pp. 57-62. In this configuration, a back-shooting technique refers to an ink ejection mechanism in which an ink droplet is ejected in a direction opposite to the direction in which a bubble expands.
As shown in FIG. 2, in the back-shooting type printhead, a heater 24 is disposed around a nozzle 26 formed in a nozzle plate 21. The heater 24 is connected to an electrode (not shown) for applying current and is protected by a protective layer 27 of a predetermined material formed on the nozzle plate 21. The nozzle plate 21 is formed on a substrate 20 and an ink chamber 23 is formed for each nozzle 26 in the substrate 20. The ink chamber 23 is in flow communication with an ink channel 25 and is filled with ink 29. The protective layer 27 for protecting the heater 24 is coated with an anti-wetting layer 30, thereby repelling the ink 29. In the ink ejector configured as described above, if current is applied across the heater 24, the heater 24 generates heat to form a bubble 28 within the ink 29, thereby filling the ink chamber 23. Then, the bubble 28 continues to expand by the heat supplied from the heater 24 and exerts pressure on the ink 29 within the ink chamber 23, thus causing the ink 29 near the nozzle 26 to be ejected through the nozzle 26 in the form of an ink droplet 29xe2x80x2. Then, ink 29 is absorbed through the ink channel 25 to refill the ink chamber 23.
However, the conventional back-shooting type ink-jet printhead has a problem in that a significant percentage of heat generated by the heater 24 is conducted and absorbed into portions other than the ink 29, such as the anti-wetting layer 30 and the protective layer 27 near the nozzle 26. It is desirable that the heat generated by the heater be used for boiling the ink 29 and forming the bubbles 28. However, a significant amount of heat is absorbed into other portions and the remainder of heat is actually used for forming the bubbles 28, thereby wasting energy supplied to form the bubble 28 and consequently degrading energy efficiency. This also increases the period from formation to collapse of the bubble 28. Thus, it is difficult to operate the ink-jet printerhead at a high frequency.
Furthermore, the heat conducted to other portions significantly increases the temperature of the overall printhead as a print cycle runs thereby making long-time stable operation of the printhead difficult due to significant thermal problems. For example, the heat produced by the heater is easily conducted to the surface near the nozzle 26 to increase the temperature of that portion excessively, thereby burning the anti-wetting layer 30 near the nozzle 26 and changing the physical properties of the anti-wetting layer 30.
In an effort to solve the above problems, it is a feature of an embodiment of the present invention to provide a bubble-jet type ink-jet printhead with a structure that satisfies the above-mentioned requirements and has an adiabatic layer disposed around a heater so that energy supplied to the heater for bubble formation may be effectively used, as well as provide a manufacturing method thereof.
Accordingly, an embodiment of the present invention provides a bubble-jet type inkjet printhead including: a substrate integrally having a manifold for supplying ink, an ink chamber filled with ink to be ejected, and an ink channel for supplying ink from the manifold to the ink chamber; a nozzle plate on the substrate, the nozzle plate having a nozzle through which ink is ejected at a location corresponding to a central portion of the ink chamber; a heater formed in an annular shape on the nozzle plate and centered around the nozzle of the nozzle plate; an electrode, electrically connected to the heater, for applying current to the heater; and an adiabatic layer formed on the heater for preventing heat generated by the heater from being conducted upward from the heater.
Preferably, the adiabatic layer is centered around the nozzle in the shape of an annulus to cover the heater and the adiabatic layer is wider than the heater.
Furthermore, the adiabatic layer may have a space filled with air or vacuum.
Due to the presence of the adiabatic layer, most of the heat generated by the heater is transferred down to ink, thereby increasing energy efficiency and operating frequency while allowing for long-time stable operation of the printhead.
The present invention also provides a method of manufacturing a bubble-jet type ink-jet printhead including: forming a nozzle plate on a surface of a substrate; forming a heater having an annular shape on the nozzle plate; etching a bottom side of the substrate and forming a manifold for supplying ink; forming an electrode electrically connected to the heater on the nozzle plate; etching the nozzle plate and forming a nozzle having a diameter less than the diameter of the heater on the inside of the heater; forming an adiabatic layer on the heater in the shape of an annulus; etching the substrate exposed by the nozzle and forming an ink chamber; and etching the substrate and forming an ink channel for supplying ink from the manifold to the ink chamber.
Forming the adiabatic layer may include: forming an annular sacrificial layer on the heater; forming an annular slot on the sacrificial layer and exposing a portion of the sacrificial layer; and etching the sacrificial layer through the annular slot and forming the adiabatic layer having an interior space from which material has been removed.
Preferably, forming the adiabatic layer further includes sealing the adiabatic layer by cogging up the annular slot with a predetermined material layer. Also preferably, sealing the adiabatic layer is performed by means of low-pressure chemical vapor deposition (LPCVD) so that the adiabatic layer is maintained substantially in a vacuum state.
According to the present invention, the/substrate integrally includes the ink chamber, the ink channel, and the ink supply manifold, and furthermore, the nozzle plate, the heater, and the adiabatic layer are integrally formed on the substrate, thereby allowing for a simple fabricating process and high volume production of printhead chips.
Another embodiment of the present invention provides a bubble-jet type inkjet printhead formed on a silicon-on-insulator (SOI) wafer including a first substrate, an oxide layer stacked on the first substrate, and a second substrate stacked on the oxide layer. The ink-jet printhead of that embodiment includes: a manifold for supplying ink, an ink chamber having a substantially hemispherical shape filled with ink to be ejected, and an ink channel for supplying ink from the manifold to the ink chamber, wherein the manifold, the ink chamber, and the ink channel are integrally formed on the first substrate; a nozzle, formed at a location of the oxide layer and the second substrate corresponding to a central portion of the ink chamber, for ejecting ink; an adiabatic barrier formed on the second substrate for forming an annular heater centered around the nozzle by limiting a portion of the second substrate in the form of an annulus; a heater protective layer stacked on the second substrate for protecting the heater; and an electrode, formed on the heater protective layer and electrically connected to the heater, for applying current to the heater.
Preferably, the adiabatic barrier is formed along inner and outer circumferences to surround the heater, thereby insulating the heater from other portions of the second substrate. Preferably, the adiabatic barrier is formed in the shape of an annular groove and is sealed by the heater protective layer so that the interior space thereof is maintained in a vacuum state. Furthermore, the adiabatic barrier may be formed of predetermined insulating and adiabatic material.
The bubble-jet type ink-jet printhead configured as described above uses the adiabatic barrier to suppress the heat generated by the heater from being conducted to another portion, thereby increasing energy efficiency. Furthermore, the bubble-jet type ink-jet printhead provides for an ink ejector having a more robust structure on the SOI wafer.
The present invention also provides a method of manufacturing a bubble-jet type ink-jet printhead using an SOI wafer. The manufacturing method includes: preparing the SOI wafer having a first substrate, an oxide layer stacked on the first substrate, and a second substrate stacked on the oxide layer; etching the second substrate and forming an adiabatic barrier having the shape of an annular groove limiting an annular heater; forming a heater protective layer on the second substrate for protecting the heater and sealing the adiabatic barrier; forming an electrode electrically connected to the heater on the heater protective layer; etching a bottom side of the first substrate and forming a manifold for supplying ink; sequentially etching the heater protective layer, the second substrate, and the oxide layer on the inside of the heater with a diameter less than that of the heater and forming a nozzle; etching the first substrate exposed by the nozzle and forming an ink chamber having a substantially hemispherical shape; and etching the first substrate and forming an ink channel for supplying ink from the manifold to the ink chamber.
Preferably, the adiabatic barrier is formed along inner and outer circumferences to surround the heater, thereby insulating the heater from another portion of the second substrate. Forming the heater protective layer is performed by means of LPCVD so that the adiabatic barrier is maintained substantially in a vacuum state.
According to this embodiment of the present invention, components of the ink ejector are integrally formed on the SOI wafer, thereby allowing for a simple fabricating process and high volume production of printhead chips.